Examine source code of Slack hide panes

{
  "manifest_version": 2,
  "name": "Slack hide panes",
  "version": "2.1",
  "description": "Hide Slack Panes.",
  "applications": {
    "gecko": {
      "id": "slack-hide-pane@javascript.ru"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.slack.com/*"
      ],
      "js": [
        "slack-hide-panes.js"
      ],
      "css": [
        "slack-hide-panes.css"
      ]
    }
  ]
}